Washington, August 13 : A research team at Worcester Polytechnic Institute (WPI) in the US are developing a solar collector that could turn roads and parking lots into inexpensive sources of electricity and hot water.
The research project, directed by Rajib Mallick, associate professor of civil and environmental engineering at WPI, aims at evaluating the potential for transforming stretches of asphalt into a cost-effective energy source.
The study looks not only at how well asphalt can collect solar energy, but at the best way to construct roads and parking lots to maximize their heat-absorbing qualities.
According to Mallick, asphalt has a lot of advantages as a solar collector.
"For one, blacktop stays hot and could continue to generate energy after the sun goes down, unlike traditional solar-electric cells," he said.
"In addition, there is already a massive acreage of installed roads and parking lots that could be retrofitted for energy generation, so there is no need to find additional land for solar farms," he added.
Roads and lots are typically resurfaced every 10 to 12 years and the retrofit could be built into that cycle. Extracting heat from asphalt could cool it, reducing the urban 'heat island' effect, according to Mallick.
"Finally, unlike roof-top solar arrays, which some find unattractive, the solar collectors in roads and parking lots would be invisible," he said.
Mallick and his research team, which also includes Sankha Bhowmick of UMass, Dartmouth, studied the energy-generating potential of asphalt using computer models and by conducting small- and large-scale tests.
The tests were conducted on slabs of asphalt in which were imbedded thermocouples, to measure heat penetration, and copper pipes, to gauge how well that heat could be transferred to flowing water.
Hot water flowing from an asphalt energy system could be used "as is" for heating buildings or in industrial processes, or could be passed through a thermoelectric generator to produce electricity.
In the lab, small slabs were exposed to halogen lamps, simulating sunlight. Larger slabs were set up outdoors and exposed to more realistic environmental conditions, including direct sunlight and wind.
The tests showed that asphalt absorbs a considerable amount of heat and that the highest temperatures are found a few centimeters below the surface.
Experimenting with various asphalt compositions, the team found that the addition of highly conductive aggregates, like quartzite, can significantly increase heat absorption, as can the application of a special paint that reduces reflection.
According to Mallick, the team concluded that the key to successfully turning asphalt into an effective energy generator will be replacing the copper pipes used in the tests with a specially designed, highly efficient heat exchanger that soaks up the maximum amount of the heat absorbed by asphalt.